Radiotelephone systems include a radiotelephone, such as a mobile station, operatively coupled to a central device, such as a base station subsystem. The radiotelephone communicates with the central device over signaling channels. A signaling channel in a bi-directional radio frequency (RF) analog system, such as a cellular system, and more particularly an advanced mobile phone system (AMPS) or narrow advanced mobile phone system (NAMPS), is a particular pair of frequency bands. A first, lower, signal bandwidth is used for the transmit path, from the radiotelephone to the base station, and a second, higher, bandwidth is used for the receive path, from the base station to the radiotelephone. The base station manages communication links with radiotelephones within its coverage area, which is commonly known as a cell. This link management includes assigning channels to the radiotelephones and initiating inter base station handoff.
Inter base station handoff in cellular systems is handoff of a radiotelephone communication link from a first base station to second base station. This handoff procedure is initiated by the first base station when the received signal strength indicator (RSSI) measurements for signals received by this base station fall below a desired level. The handoff is accomplished between the first and second base stations according to a known protocol. The handoff protocol that is typically used in analog cellular radiotelephone systems considers the direction of travel of the radiotelephone in the cellular service area. When the signal strength is weak, and the radiotelephone is moving to an edge of a cell, the hand off-is initiated by the first base station. Thus, the handoff is a base station initiated action. However, this protocol does not accommodate inter base station changes, which are changes to other channels of the base station, or take into consideration the signal strength of signals transmitted to the radiotelephone in initiating a channel change, or permit a user to request a channel change.
Some time division multiple access (TDMA) digital cellular system include mobile assisted handoff. In these systems, the radiotelephone periodically measures the signal strength of the radiotelephone receive paths of different channels for use in handoff procedures. The measured signal strength is transmitted to the base station. The base station makes inter base station handoff decisions based in part on these channel measurements received from the radiotelephone. However, the system does not permit the user to request a channel change at any time based upon the user's perceived received signal quality.
In cordless radiotelephones, the user can initiate a channel change for the RF link between a handset and its dedicated base, which base is connected to a land-line telephone system. The channel change is initiated using a key in the handset. When the user actuates the key, a signal is communicated to the base that controls the base to select the next sequential channel that is not in use. Although this system works well for a cordless telephone handset which is dedicated to the base and has a very limited number of possible channels (such as ten channels), channel change requests only result in rotation through each of the channels in a predetermined, fixed sequence.